1. Field of the Invention
This invention relates to a reproducing apparatus and, more particularly, to an apparatus for duplicatingly reproducing still images, for instance.
2. Related Background Art
It has been a practice to let a video signal supplied to an apparatus be tentatively stored in a memory and to let a signal read out from the memory be output to a monitor or to a printer.
Heretofore, however, where a memory used for a monitor or printer is also used for other purposes or where separate memories are provided, the contents of such two memories are altered continuously. Therefore, there is a problem in case of printing out data using a printer that an image signal supplied to the apparatus during printing is wasted.
In a different aspect, recently proposed broadcast television systems intended for practical use, aside from the conventional NTSC system with an aspect ratio of 3:4 and a scanning line number of 525, include those of finer resolution, for instance a HDTV system with an aspect ratio of 9:16 and a scanning line number of 1,125. The HDTV system can deal with about five times the image data quantity compared to the NTSC system and also uses a wide screen. Thus, it permits enjoyment of images which are dense and rich in the on-the-spot senser.
However, data quantity has been increased to such an extent that it can not be directly transmitted to each home due to limitations imposed on the broadcast waves and communication capacity. Therefore, bandwidth compression is adopted for transmission on the basis of commonly termed distribution quality, which is slightly inferior to the intrinsic image quality obtained in the studio. Table 1 shows specifications concerning the in studio quality and distribution quality in the HDTV system.
TABLE 1 ______________________________________ In-studio Distribution quality quality ______________________________________ Scanning line 1,125 1,125 number Brightness 30 MHz 20 MHz bandwidth (Y) Brightness 74.25 MHz 48.6 MHz sampling frequency Chromatic 15 MHz 7 MHz difference bandwidth (Pr, Pb) Chromatic 37.125 MHz 16.2 MHz difference sampling frequency ______________________________________
It is thus inevitable to provide distribution quality for home enjoyment of HDTV system images as moving images.
In the meantime, with the HDTV system the scanning line number is large, and the image is dense and less subject to flickering. For this reason, the HDTV system image is enjoyable as a still image rather than as moving images, and utilization of the HDTV system in the fields of art, culture, education and animation has been expected. In the case of a still image, the observer looks at one frame of an image thoroughly in several to several tens of seconds. For this reason, in-studio quality is required as image quality.
Accordingly, a HDTV still image reproduction apparatus permitting enjoyment of in-studio quality is proposed separately from the HDTV distribution quality image reproduction apparatus. FIG. 4 shows a block diagram of an example of such a structure. Reference numeral 10 designates an antenna for receiving signals transmitted from a broadcast satellite, 12 is a HDTV still image reproduction apparatus, 14 is a HDTV color image monitor for displaying images with 1,125 scanning lines. In this still image reproduction apparatus, reference numeral 16 designates a tuner for converting signals received by antenna 10 into still image digital compression data, 18 is a decoder for decoding still image digital compression data obtained by, for instance, bandwidth compression in a DPCM process, into original image data, 20 and 22 are image frame memories each for storing one frame of decoded image data from decoder 18, 24 is a switch for selecting image frame memory 20 or 22 for writing decoded data from decoder 18, 26 is a switch for selecting image frame memory 20 or 22 for reading out stored data, and 28 is a D/A converter for converting image data read out from image frames 20 and 22 into an analog signal.
In this still image system, signals intercepted by antenna 10 are converted by tuner 16 into digitally compressed data, which is then decoded by decoder 18. Decoded data from decoder 18 is written in alternate image frame memories 20 and 22 under control of switch 24, and data read out from image frame memories 20 and 22 are supplied to D/A converter 28 and printer 13 alternately under control of switch 26. In other words, switches 24 and 26 function such that decoded data is written in one image frame memory (for instance 20) while stored data is read out from the other image frame memory (for instance 22).
As to the transmission rate, since one still image frame is observed in several to several tens of seconds, it is usually about 2 Mbps for saving the transmission bandwidth (here the bit rate of the transmission).
In the still image system, if it is desired to obtain a hard copy of the received image on a recording sheet or the like using printer 13, during transfer of data to printer 13 one of the image frame memories 20 and an 22 is occupied, and image from the other image frame memory can not be observed on monitor 14.